Documents that have disclosed a technology for improving responsiveness in controlling the start of an engine by using a motor generator, for example, include Patent Literature 1 described below.
Patent Literature 1 discloses a technology in which, when an engine restart (reactivation) command is issued, a controller cranks an engine by using a motor generator, after the rotational speed of the engine has reached a predetermined rotational speed, performs rotational speed feedback control of the engine, resumes fuel injection to the engine and spark ignition, determines combustion stability of the engine on the basis of regenerative torque required of the motor generator, and, when determining that the engine changes to a stable combustion state, switches a feedback gain to a relatively small feedback gain.